1. Field of the Invention
The invention relates to a radiation-sensitive composition.
2. Discussion of the Background
In the field of microfabrication represented by fabrication of integrated circuit elements, in order to obtain a higher degree of integration, the miniaturization of processing size in lithography is progressing. However, it is extremely difficult to form a fine pattern of no more than 0.3 μm with high accuracy by a conventional method using a visible light ray (wavelength: 800 to 400 nm) or a near ultraviolet ray (wavelength: 400 to 300 nm). Therefore, the use of deep ultraviolet rays represented by KrF excimer (wavelength: 248 nm) laser, ArF excimer laser (wavelength: 193 nm) and the like, X rays such as synchrotron radiation, charged particle rays such as electron beam has been studied intensively. Of these, especially, the lithography using an excimer laser has already been put into practical use and has been applied widely in manufacturing integrated circuit elements because of its high output, high efficiency and others.
And, as a resist suitable for deep ultraviolet rays such as an excimer laser, a “chemically amplified resist” has been used, in which, a radiation-sensitive acid generator which generates an acid by irradiation of radiation (hereinafter referred to also as “exposure”) is used and the catalytic action of the acid improves the sensitivity of the resist.
As such a chemically amplified resist, for example, Japanese Patent Application Laid-open No. S59-45439 discloses the combination of a resin protected by a t-butyl group or a t-butoxycarbonyl group and a radiation-sensitive acid generator; Japanese Patent Application Laid-open No. S60-52845 discloses the combination of a resin protected by a silyl group and a radiation-sensitive acid generator. Further, as for chemically amplified resists, there are many other reports including Japanese Patent Application Laid-open No. H02-25850 disclosing a resist containing a resin having an acetal group and a radiation-sensitive acid generator.
However, due to the increasing complexity of integrated circuit element structure in recent years, in forming transistors having a three-dimensional structure represented by the Fin-FET or the like, lithography processes for patterning a resist pattern on a substrate having steps of polysilicon or the like have increased. In such a process, at the time of exposure, an insufficient amount of light which reaches the foot of the step causes a problem that the solubility of the resist at the exposed area is low and an undissolved residue of the resist (hereinafter referred to as scum) is left. Particularly, in the lithography process for forming a resist pattern for an ion implantation mask in which a lower-layer antireflection film cannot be used, as coupled with the effects of standing waves due to reflection from the substrate, applying conventional resist materials is becoming difficult, and a resist which better prevents a scum from being left has become demanded.